2001 C5 Unknown Engine Noise

A few weeks back, the car developed a rattle/tap/low pitched squeak type noise coming from what sounds like the front of the engine. It's not really present at idle, but appears at about 1000rpm and increases relative engine speed. It's does not sound like a rhythmic valvetrain tap, or a bottom end knock (it's quieter than that), and the engine runs healthy, smooth, and throws no codes, but it's definitely a noticeable noise.

After tons of searching and diagnosing, and finding a wobbling harmonic balancer, I went ahead and replaced it, thinking I had the culprit. But once I got it back assembled enough to re-start the car, the noise was exactly the same. I ran the car with the drive belts off, so none of the other accessories were turning. But, the noise remained unchanged.

I'm now thinking that the problem could be behind the timing cover. I've read about stock LS1 engines having the cam bolts back out, hit the timing cover, eventually shear off and crash the valvetrain, but I have never heard of anything like that outside of these forums. Is there anyone around that has had experience with these cam bolts backing out BEFORE the catastrophic failure happens? The theory now is that maybe what I'm hearing is the beginnings of that problem.

I also know that the oil pump is located on the front of the crankshaft, so that could be another possibility. I've never heard about the oil pumps in these engines making noise, but I checked out a new pump and the bearing that goes around the crank definitely has a rattle type sound when you wobble it. So, I suppose that's another possibility.

Hopefully some of your Corvette guru's might have some light to shed on the subject, because I'm quickly approaching the end of my rope.

The engine is bone stock with about 83k easily driven on the odometer.

Thanks all.

 

I had tapping noise one time. Turns out one of my spark plugs started backing out.

 

Can you post a video with the sound it's making?

 

Tapping could be anything but first thought is a lifter. How many miles on the clock?

 

Is the noise noticeable inside the car or only standing in front of it with the hood open?

 

I'm on my mobile so I'm limited. Do a search on my user name and "rattle". See if this sounds like your problem.

I have a feeling you have bad lifters like I did. If you do, plan to replace your oil pump as mine was chewed up from pumping lifter shrapnel.

 

 

My anecdote. I had a similar strange sound on my Subaru with your exact symptoms. Turned out to be an exhaust weld had corroded and was allowing the exhaust to flop around. Sounded terrible and was a pretty strange sound. Look up H pipe jingle on the forums and see if that matches your sound.

 

 

check the tensioner pulley.
I call the sound rabid cricket...easier to pick off at idle or when next to something that will echo.
Once engine speeds picks up, road noise makes it much more difficult to hear

 

Sounds dumb but turn the A/C on and off and see if it changes the sound.